Phytases (myo-inositol hexakisphosphate phosphohydrolase: EC 3.1.3.8) are enzymes that hydrolyze phytate (myo-inositol hexakisphosphate) to myo-inositol and inorganic phosphate. The enzymes are known to be valuable feed additives. At the close of the twentieth century, annual sales of phytase as an animal feed additive were estimated to be $100 million and growing.
Poultry and pig diets are currently based primarily on cereals, legumes, and oilseed products. About two-thirds of phosphorus (P) present in these feedstuffs occur as phytates, the salts of phytic acid (myo-inositol hexakisphosphate, InsP6) (Jongbloed et al., 1993). Phytate phosphorus in plants is a mixed calcium-magnesium-potassium salt of phytic acid that is present as chelate and its solubility is very low (Pallauf and Rimbach, 1997). Phosphorus in this form is poorly digestible/available for monogastric animals such as human, swine, and poultry.
For the utilization of phytate phosphorus and minerals and trace elements bound in phytic acid complexes, hydrolysis of the ester-type bonded phosphate groups of phytic acid by phytase is necessary (Rimbach et al., 1994). Phytases belong to a special group of phosphatases which are capable of hydrolyzing phytate to a series of lower phosphate esters of myo-inositol and phosphate. Two types of phytases are known: 3-phytase and 6-phytase, indicating the initial attack of the susceptible phosphate ester bond. Although monogastric animals lack sufficient phytase to effectively utilize phytate phosphorous, many fungi, bacteria and yeasts produce phytase that can be used to supplement animal rations.
The beneficial effects of supplementary phytases on phosphorus digestibility and animal performance have been well documented (Mroz et al., 1994; Kornegay et al., 1996; Rao et al., 1999; Ravindran et al., 1999). However, most of these studies have been performed on an ad hoc basis with often only superficial information of the enzymes provided as marketing strategies by the manufacturers. The efficacy of any enzyme preparation depends not only on the type, inclusion rate and level of activity present, but also on the ability of the enzyme to maintain its activity in the different conditions encountered through the gastrointestinal tract and the conditions used for the pre-treatment of a food or feed formulation.
Although numerous phytases are available for use as supplements, many of the enzymes have certain disadvantages. For example, many of the currently used phytases lose activity during feed pelleting process due to heat treatment. Additionally, many of the currently used phytases are not adequate in diets containing low levels of supplemental calcium phosphate. In addition, in many instances, there is a high cost of production associated with the microbially expressed enzymes.
Thus, what is needed is a phytase with improved properties for animal feed and food processing as well as an economical procedure for producing the phytase. One method of producing a more economical phytase would be to use recombinant DNA techniques to produce transgenic plants or plant organs capable of expressing phytase which could then be added as such to animal feed or human food for direct consumption. Alternatively, the phytase could be extracted and, if desired, purified for the desired application.